jgo 3.1.0

Launch Java code from Python and the CLI, installation-free.

jgo: painless Java environments and execution

Summary

jgo launches Java applications directly from Maven coordinates—no installation required. Specify a Maven artifact identifier and an optional main class, and jgo resolves dependencies, materializes the environment including the version of Java needed, and runs your program.

# Run Jython REPL (latest version)
jgo org.python:jython-standalone

# Run with specific version
jgo org.python:jython-standalone:2.7.3

Features

• Zero-configuration execution: Automatic Java download and version management thanks to cjdk integration
• Pure Python dependency resolver: No Maven installation required to resolve dependency graphs
• Reproducible environments: jgo.toml project files with lock files (like package.json + package-lock.json)
• Three-layer architecture: Independently useful layers for Maven resolution, environment building, and execution
• Powerful Python API: Fine-grained control over dependency resolution and execution
• Intelligent module handling: Full support of the Java module system (JPMS), including intelligent classification of dependencies on module-path or class-path as appropriate

Quick Start

CLI Usage

# Run Jython REPL
jgo org.python:jython-standalone

# Run with arguments
jgo org.python:jython-standalone -- -- script.py --verbose

# Multiple artifacts with main class (use @ separator)
jgo org.scijava:scijava-common+org.scijava:scripting-jython@ScriptREPL

# Force update from remote repos
jgo -u org.python:jython-standalone

# Use specific Java version
jgo --java-version 17 net.imagej:imagej

# Print classpath without running
jgo info classpath org.python:jython-standalone

# Preview commands without executing (--dry-run)
jgo --dry-run run org.scijava:parsington         # See java command
jgo --dry-run init org.python:jython-standalone  # Preview jgo.toml

Python API

import jgo

# Simple one-liner
jgo.run("org.python:jython-standalone:2.7.3", app_args=["script.py"])

# Build environment without running
env = jgo.build("org.python:jython-standalone")
print(env.classpath)  # List of JAR paths

# Resolve dependencies
components = jgo.resolve("org.python:jython-standalone")
for comp in components:
    print(f"{comp.groupId}:{comp.artifactId}:{comp.version}")

Project Mode with jgo.toml

Create reproducible environments:

# jgo.toml
[environment]
name = "my-java-app"

[repositories]
scijava.public = "https://maven.scijava.org/content/groups/public"

[dependencies]
coordinates = ["net.imagej:imagej:2.15.0"]

[entrypoints]
default = "main"
main = "net.imagej.Main"

[settings]
cache_dir = ".jgo"  # Local environment like .venv

# Run from current directory
jgo sync

# Creates .jgo/ with jars/ and jgo.lock.toml

Installation

Installing jgo with uv

uv tool install "jgo[cli]"

Installing jgo with pip

pip install "jgo[cli]"

Installing jgo with conda

conda install -c conda-forge jgo

Installing jgo from source

git clone https://github.com/apposed/jgo
uv tool install --with-editable "jgo[cli]" jgo

When installed in this fashion, changes to the jgo source code will be immediately reflected when running jgo from the command line.

Using jgo as a library dependency

uv add jgo

or

pixi add jgo

Not sure which to use? Read this.

The cli extra (jgo[cli]) is only needed when using the jgo command-line tool, not when using jgo as a Python library.

Examples

Program	Command
Jython REPL	jgo org.python:jython-standalone
JRuby eval	echo "puts 'Hello Ruby'" | jgo org.jruby:[e-mail]
Groovy REPL	jgo org.codehaus.groovy:groovy-groovysh+commons-cli:commons-cli:[e-mail]

Note the usage of the + syntax as needed to append elements to the classpath.

If you add scijava.public = https://maven.scijava.org/content/groups/public to the [repositories] section of your settings file (see the configuration docs), you can also try:

Program	Command
SciJava REPL with JRuby	jgo org.scijava:scijava-common+org.scijava:scripting-jruby@ScriptREPL
SciJava REPL with Jython	jgo org.scijava:scijava-common+org.scijava:scripting-jython@ScriptREPL
SciJava REPL with Groovy	jgo org.scijava:scijava-common+org.scijava:scripting-groovy@ScriptREPL
SciJava REPL with Clojure	jgo org.scijava:scijava-common+org.scijava:scripting-clojure@ScriptREPL
SciJava REPL with JavaScript	jgo org.scijava:scijava-common+org.scijava:scripting-javascript@ScriptREPL

FAQ

• Is it fast? Endpoints are synthesized in a local cache under ~/.cache/jgo. So invoking the same endpoint a second time is really quick.
• What does "no installation" mean? Classpath elements are hard-linked into ~/.cache/jgo from ~/.m2/repository rather than copied, so the cache folder has a tiny footprint even if you execute lots of different endpoints.
• What if an endpoint has a new version? Pass the -u flag to jgo to rebuild the endpoint. Note that unlike mvn, jgo does not check for updates otherwise.

Documentation

Full documentation is available at jgo.apposed.org:

• Getting Started — Installation and quick start
• CLI Reference — All commands and options
• Project Mode — Working with jgo.toml
• Python API — Using jgo from Python code
• Configuration — Repositories, shortcuts, and settings
• Migration Guide — Upgrading from jgo 1.x
• Architecture — The three-layer design

Use help(jgo) in Python for detailed API documentation.

Development

Code style

jgo uses ruff for linting and formatting:

make lint

Testing

# Run all tests
make test

# Run specific test file
bin/test.sh tests/test_maven_basic.py

# Run with coverage
uv run pytest --cov=src/jgo tests/

Alternatives

• JBang
• mvnx (unmaintained)
• JPM4J (discontinued)
• Mop (unmaintained)
• marun (unmaintained, Python 2 only)